Author Topic: FIXED: Power Designs 2005A repair  (Read 13549 times)

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Offline motocoder

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FIXED: Power Designs 2005A repair
« on: September 26, 2014, 12:54:12 am »
I have purchased a Power Designs 2005A off of eBay. While it is cosmetically in good shape, it is not working.

Upon switching the unit on, the 0-10V or 10-20V lamp (depending on the position of the switch) illuminates, but the Oven light does not come on and the meter stays at zero. The voltage across the DC+ and DC- terminals is about -0.3 volts.

Does anyone have a schematic or other technical documentation for this unit? I saw a link on one of the threads here, but the link was broken. Any advice on where to start troubleshooting?

Thanks
« Last Edit: October 07, 2014, 07:12:27 am by motocoder »
 

Offline robrenz

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Re: Power Designs 2005A repair
« Reply #1 on: September 26, 2014, 01:06:14 am »
PM me your email and I will send you a pdf of the 2005A manual

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #2 on: September 26, 2014, 01:44:47 am »
PM me your email and I will send you a pdf of the 2005A manual

PM sent. Thanks!
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #3 on: September 26, 2014, 02:36:04 am »
ok, internal fuse was blown. i don't have an exact replacement, but i had a smaller amperage fuse. I put that in and now I am getting something on the output. It seemed reasonably stable before i started messing with the dials, although it was about 20% below the set voltage value.

Oven light still not coming on, but that might just be the neon lamp.

I will definitely need to clean the contacts on the switches - anyone have a recommendation on how to go about that?
« Last Edit: September 26, 2014, 07:12:13 am by motocoder »
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #4 on: September 26, 2014, 07:21:21 am »
Ok, have a few more data points now.

The oven lamp is actually fine. The SCR that switches the voltage reference heater on/off is never switching on. This is because its gate is never going high. I briefly shorted its anode to gate, and i saw the lamp light up (this might have been dumb as i may have damaged Q11)

So next I need to determine why the SCR is not being switched on. My suspicion is the thermostat is bad, or possibly Q11 (or maybe both if I damaged Q11 in my testing).
 

Offline robrenz

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Re: Power Designs 2005A repair
« Reply #5 on: September 26, 2014, 11:09:05 am »
I will definitely need to clean the contacts on the switches - anyone have a recommendation on how to go about that?

Link to part of the POWER DESIGNS thread here

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #6 on: September 26, 2014, 01:17:16 pm »
I will definitely need to clean the contacts on the switches - anyone have a recommendation on how to go about that?

Link to part of the POWER DESIGNS thread here

Thanks, I orderd some DeOxIt D100L and G100L. Where you say to first wash with a "general electronic cleaner" and to "wash the D100L off" - what do you recommend for that?
 

Offline robrenz

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Re: Power Designs 2005A repair
« Reply #7 on: September 26, 2014, 01:25:09 pm »
I use CRC Lectra-Motive from the auto parts store.

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #8 on: September 26, 2014, 01:31:02 pm »
I use CRC Lectra-Motive from the auto parts store.

thanks. Also, per the thread you linked, I also need to re-lube/grease the non-contact parts of the switches where things move against each other. What do you recommend for that?
 

Offline robrenz

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Re: Power Designs 2005A repair
« Reply #9 on: September 26, 2014, 01:39:23 pm »
Any light grease will work. I used TriFlow synthetic grease just because I had some on hand.

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #10 on: September 27, 2014, 09:26:38 am »
I did some more investigation this evening. I also created a little LTSpice simulation to better understand how the heater circuit works.

Anyway, one of the things I tried tonight was to place a diode across the SCR anode/cathode, effectively removing it from the circuit. While I did this, I measured the voltage across the thermostat (terminals 9 and 11 on the the heater connection on the bottom of the PCB). The thermostat is "on" (shorted) when the meter starts up, but it never goes off. Also, the little heater tube never felt like it was getting warm at all.

So this prompted me to measure the resistance of the heater by taking a measurement across terminals 9 and 10. OPEN CIRCUIT. So I think the heater may be burned out. I also suspect the SCR is not good, but will follow up on the heater first.

BTW - does anyone know approximately what resistance I should see across the two heater terminals?
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #11 on: September 27, 2014, 09:49:06 am »
Started taking the heater tube apart. Big mistake. I am wondering if the insulation inside this thing is asbestos  :o
 

Offline David Hess

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Re: Power Designs 2005A repair
« Reply #12 on: September 27, 2014, 10:31:24 am »
I would expect it to just be fiberglass.
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #13 on: September 27, 2014, 03:24:54 pm »
Inside the outer aluminum tube. embedded in some tape was a coil od wire, wound around the outsode of the inner tube. I wonder if this was the heater coil?

Anyone have any insight into what I should see insode this tube?
 

Online SeanB

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Re: Power Designs 2005A repair
« Reply #14 on: September 27, 2014, 03:40:32 pm »
That was the heater, made with nichrome wire. Inside will be the diode voltage reference. You can rewind the heater with new wire, or repair the break if you did not damage the wire undoing it. The tape is Kapton tape to provide insulation for the windings, as they typically use an uncoated wire for the heater.
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #15 on: September 27, 2014, 05:13:59 pm »
That was the heater, made with nichrome wire. Inside will be the diode voltage reference. You can rewind the heater with new wire, or repair the break if you did not damage the wire undoing it. The tape is Kapton tape to provide insulation for the windings, as they typically use an uncoated wire for the heater.

Ok, thanks
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #16 on: September 27, 2014, 10:25:28 pm »
Ok, I have ruined the heater assembly trying to get it fully apart. I thought by removing the internal screws, the tube would come off the connector, but I couldn't get it off there.  The little board that goes inside the heater tube is completely intact, but the tube will need some rework, and the heater wire needs to be replaced.
« Last Edit: September 28, 2014, 01:34:42 pm by motocoder »
 

Offline David Hess

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Re: Power Designs 2005A repair
« Reply #17 on: September 28, 2014, 12:01:08 am »
I wish I was close to Seattle.

Wouldn't replacing the oven stabilized reference with a modern integrated series or shunt reference be easy and perform about as well?
 

Online SeanB

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Re: Power Designs 2005A repair
« Reply #18 on: September 28, 2014, 05:54:30 am »
I have a roll of thin nichrome wire, which probably would work as a replacement heater unit if wound carefully. Want to put it in a parcel and send sea post ( not air as those are heavy) to South Africa? Sea post would probably arrive after the post office strike here is over.
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #19 on: September 28, 2014, 06:40:56 am »
I have a roll of thin nichrome wire, which probably would work as a replacement heater unit if wound carefully. Want to put it in a parcel and send sea post ( not air as those are heavy) to South Africa? Sea post would probably arrive after the post office strike here is over.

I ordered some Nichrome wire from Amazon. I will give repairing it another try unless someone local here comes to claim it first.

i also need to figure out what to use to replace the various layers of different kinds of tape that were on that tube. I think the outer insulation was or could be replaced with Scotch glass cloth tape, and held together with kapton tape. The innermost layer was some sort of almost clear plasticy stuff. Probably something that conducts heat well. Silicon tape maybe?
 

Online SeanB

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Re: Power Designs 2005A repair
« Reply #20 on: September 28, 2014, 07:16:52 am »
Inner was likely a PTFE clear shrink or just a sleeve, and then the wire, then kapton tape (transparent yellow) to hold it down then a covering of glass tape, then you would have a glass or rock wool insulating layer then a light binding layer of kapton to allow it to be easily inserted into the outer housing. Original might have used asbestos fibre as insulation if it was made before 1975 or so.
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #21 on: September 28, 2014, 07:24:23 am »
Inner was likely a PTFE clear shrink or just a sleeve, and then the wire, then kapton tape (transparent yellow) to hold it down then a covering of glass tape, then you would have a glass or rock wool insulating layer then a light binding layer of kapton to allow it to be easily inserted into the outer housing. Original might have used asbestos fibre as insulation if it was made before 1975 or so.

Everything you describe sounds exactly like what I removed, with the exception of the innermost layer. The innermost layer was a strip about 10-15mm in width, wrapped diagonally around the tube. It was not very sticky if at all. I think the real question is a reasonably obtainable minimum set of stuff that I need to restore this thing. It will be easy to spend more than the cost of this item in nichrome wire, tape, and contact cleaner (the contact cleaner I am OK with, as I am sure I will use that on many projects)
 

Online SeanB

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Re: Power Designs 2005A repair
« Reply #22 on: September 28, 2014, 07:34:06 am »
Then it was plain ptfe strip, you can use the kapton tape in it's place as it will withstand the heat of the wire.

One small roll of nichrome wire, a roll of kapton tape ( useful for many things), a roll of glass cloth tape 9 can be used to replace the glass wool if you wind a few loose layers on in place of it) and a soldering iron and solder to attach the nichrome wires to fly leads after sanding the ends with 1200 grit sandpaper to clean them. Take a small piece of sandpaper, fold in half and wipe the lead gently around 10 times to remove any oxide layer and roughen it, then solder it immediately after wrapping it around the flylead. Might not solder easily but should have good enough mechanical contact buried in solder.
 

Offline motocoder

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Re: Power Designs 2005A repair
« Reply #23 on: September 28, 2014, 07:44:10 am »
Then it was plain ptfe strip, you can use the kapton tape in it's place as it will withstand the heat of the wire.

One small roll of nichrome wire, a roll of kapton tape ( useful for many things), a roll of glass cloth tape 9 can be used to replace the glass wool if you wind a few loose layers on in place of it) and a soldering iron and solder to attach the nichrome wires to fly leads after sanding the ends with 1200 grit sandpaper to clean them. Take a small piece of sandpaper, fold in half and wipe the lead gently around 10 times to remove any oxide layer and roughen it, then solder it immediately after wrapping it around the flylead. Might not solder easily but should have good enough mechanical contact buried in solder.

Ok, that sounds quite reasonable and except for the glass cloth tape, is all stuff I will use again. I do have some PTFE tape here as it turns out - I use it seal threads for air and water connections. Do you think a thin layer of that would conduct heat into the tube better than the kapton?
 

Online SeanB

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Re: Power Designs 2005A repair
« Reply #24 on: September 28, 2014, 07:49:34 am »
Would not trust that tape as insulation, it tears too easily. The kapton tape will do for that.
 


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